The present invention relates to a method for producing a highly pure solution containing hydrogen fluoride (HF), a salt thereof, or a mixture thereof, wherein hydrogen fluoride is introduced into an anhydrous solvent as a gas and/or as a liquefied gas.
The electronics and semiconductor industries, among others, require highly pure process solutions. Among these solutions, are solutions containing HF, HF salts or mixtures thereof, with or without other ingredients.
Ammonium fluoride solutions, for which among the highest purity requirements are imposed, are generally produced by dissolving crystalline ammonium fluoride in the corresponding solvent, as is e.g. described in U.S. Pat. No. 5,320,709. One disadvantage of this method is that metallic impurities are generally within the ppm range, and the solutions are therefore inappropriate for fields of use having stricter purity requirements for metal content. The additional purification of crystalline ammonium fluorides necessary for producing highly pure solutions with a substantially lower metal content is, however, difficult.
A further disadvantage is that it is very difficult in manufacturing to obtain reproducible concentrations of free hydrogen fluoride in the ammonium fluoride solutions from batch to batch. For some industrial applications, however, constant free hydrogen fluoride content is crucial.
There remains a need for solutions of hydrogen fluoride and hydrogen fluoride salts having greater purity and for solutions of hydrogen fluoride salts in which the concentration of free hydrogen fluoride remains relatively constant from batch to batch.